This application claims priority of German Application No. 101 64 529.5, filed Dec. 18, 2001, the complete disclosure of which is hereby incorporated by reference.
a) Field of the Invention
The invention is directed to an arrangement for storing and transporting at least one optical component which is accommodated in a vessel with a vessel door which closes in a gastight manner for protection against environmental influences.
b) Description of the Related Art
It is well known that in optical lithography chip structures are transferred to a wafer by means of a mask and with light. While special lasers generate the wavelengths needed for high resolution, high-resolution projection objectives serve to image the structures, and the very high-resolution lenses contained therein are gaining importance due to increasingly smaller chip structures.
Lenses of optical glasses or quartz lasers are not suitable for the corresponding projection objectives primarily because of their low resistance to short-wave laser radiation. It is better to use lenses of high-quality calcium fluoride, although this is very susceptible to contamination, particularly by water. Even monolayers of water which are difficult to remove from the fluoride surfaces result in high absorption losses at laser wavelengths below 193 nm and particularly at 157 nm.
For this reason, the optical components in wafer steppers are surrounded by a cleanroom atmosphere in that the operation is carried out either with gas purging or under vacuum conditions.
The problem of protecting the surfaces of the optical components from impurities after their production until they are put into operation in the optical projection beam path has not been solved satisfactorily, particularly when closeable vessels are used for storage.
It is particularly problematic to maintain cleanliness when the components are to be stored initially and transferred into the projection beam path of the semiconductor fabrication plant subsequently while ensuring their readiness for immediate operation.
Therefore, it is the primary object of the invention to solve this problem, particularly to protect the optical components from contamination not only during their storage and transport, but also when installing them in operative condition in the optical projection beam path.
This object is met in an arrangement of the type mentioned above in that every optical component is fastened in an aligned manner to a carrier that is provided in the vessel, a manipulator acts on the carrier to transfer the carrier into an optical beam path enclosed by a cleanroom through an airlock opening which is formed when the vessel door is open.
The vessel door is outfitted with drivers for a closure of a loading and unloading opening of a chamber enclosing the cleanroom, which drivers engage in the closure during assembly and when opening the vessel, so that the airlock opening is released when the vessel door is pulled open perpendicular to the direction of manipulation such that the closure is carried along.
The vessel door advantageously comprises two parts which are displaceable relative to one another; a first part contains the drivers and a second part which can be fastened serves to close the vessel. The two parts have opening distances which differ from one another and are displaceable into different positions in a direction perpendicular to the manipulation of the carrier.
In a first position, the first part opens the loading and unloading opening by carrying along the closure in order for protective gas to flow out of the chamber for partial cleaning, whereas the second part closes the vessel in the fastened state. The airlock opening is released in at least one further position.
In a particularly advantageous manner, in a second position in which the fastening of the second part is canceled, the two parts of the vessel door are initially moved into a common displacement position in which the loading and unloading opening is completely open and the vessel is partly open. Finally, due to the fact that its opening excursion is greater than that of the first part, the second part occupies another displacement position in a third position in which the vessel is also completely open. A partly automatic safety mechanism which acts vertical to the displacing position and mechanically locks the first part and second part relative to the vessel can be installed in the second part.
In order to prevent pressure losses within the chamber, it is particularly advantageous when the vessel is provided with a diaphragm for limiting a gap which is formed when the vessel is opened due to a wedge-shaped construction of the second part.
In order to transfer the carrier safely and quickly with every optical component fastened thereto in an aligned manner, the manipulator should be contained in the vessel and should have an interface for attaching a lengthening manipulator arm for long transport paths. During manipulation, the carrier can be fixed in various locking positions lying in different planes and is separated from the manipulator only in these locking positions.
By means of the invention, an optical component is transferred into an installation to be loaded while retaining a defined aligned state had by the optical component in a protective atmosphere, so that it can perform its imaging function within the installation without additional alignment. The component is constantly protected against contamination during storage and also when transferred from the vessel to a cleanroom. This minimizes the risk of handling for CaF2 components.
Since the vessel is also suited for removal of the optical components from the installation, the cost-intensive optical components can be transported for further processing in this manner. The optical surfaces that are loaded by laser radiation can be re-polished and re-coated in the above-mentioned processing. The optical components that have been treated in this way are then put into the vessel again in the pre-aligned state in order to protect them from environmental influences so that, if necessary, they are available for use in one of the beam paths of an installation.
Another advantage consists in that the preadjusted components can be handled quickly and easily without stopping the system. The vessel can be connected to the installation in question in a simple manner.